You can find the full Legislation for Medical Cannabis Usage (2018) on the UK government website.
Smoking vs. Vaping
All patients are expected to vape, or consume sublingual products (oils, capsules etc.), smoking is only permitted for 'research' purposes.
According to the exact wording used in the above linked amendments to the Misuse of Drugs Act:
16A (3) A person shall not self-administer a cannabis-based product for medicinal use in humans by the smoking of the product (other than for research purposes in accordance with regulation 13)
Regulation 13 of the Misuse of Drugs Act (2001) states:
(...) shall not have effect in relation to the smoking of cannabis or cannabis resin for the purposes of research on any premises for the time being approved for the purpose under this regulation by the Secretary of State.
We interpret the current legislation as only permitting the 'smoking' of medical cannabis, when part of a research group. This is not intended to be legal advice, just but an interpretation of the above vague legalese.